Evidence suggests that ingestion of selenium compounds may inhibit carcinogenesis. We studied this in hamsters in which squamous cell carcinoma of the tongue was induced with 0.5% dimethylbenzanthracene (DMBA). Forty-five hamsters, divided into three groups of 15 each, were fed a low-selenium diet and the left lateral border of the tongue was painted with DMBA three times a week. Control animals were given deionized water, while water for animals in groups 1 and 2 contained 3 and 6 ppm selenium, respectively. All sufficiently long-lived animals developed leukoplakia of the tongue and floor of the mouth that progressed to dysplasia and papillary or ulcerative carcinoma. Carcinomas were seen less frequently on the palate and in the pyriform sinuses. Carcinoma metastasized to neck lymph nodes in two hamsters. Data indicate a 2-week delay in leukoplakia incidence for the selenium groups; a higher survival rate was also noted, although this was not statistically significant. We conclude that this model is similar to tobacco-induced squamous cell carcinoma of the upper aerodigestive tract in humans and that ingestion of supplemental selenium produces a modest inhibitory effect on leukoplakia.